It is known in the prior art to use printers with thermal printheads to produce contrasting images on a print medium such as a label stock. In one form, such printheads directly contact a thermally sensitive print medium. In others, a ribbon carrying a thermally transferrable dyed wax is placed between the printhead and a thermally insensitive print medium.
The wide applicability of such printers allows them to be used with different types of print medium, many of which use a printable material carried through the printer on a removable strip of backing material. The print medium may include separate pieces of printable material, such as self-adhesive labels, with gaps between the adjacent edges of the labels. The print medium can have many different characteristics, for example, having several different possible thicknesses.
It is important for the printer to coordinate the operation of the printhead and movement of the print medium, and especially the leading edges of the labels carried by the strip of backing material, so that the images can be placed in the desired position on the labels. Therefore it is desirable to have a printer that can sense the gaps between labels, or in other words, the leading or trailing edges of the labels, and control its operation based on the passage of the labels through the printer.